The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
Fiber-optic communications begin with the invention and applications of multimode optical fibers. Over the past decades, although single-mode optical fibers have become the main variety demanded in the optical fiber market, the multimode optical fibers have never been replaced and have maintained a steady growth in market demands. And the reason is that many characteristics of the multimode optical fibers can just meet the use of optical signals, energy transmission, local area network (LAN) data transmission and optical devices. Currently, the cost of a multimode fiber-optic communication system is far lower than that of a single mode fiber-optic communication system, which is also one of the reasons why the multimode optical fibers are everlasting. Conventional multimode optical fibers can be classified into two categories, that is, 50 μm and 62.5 μm, according to recommended standards of IEC, ITU and other international standard organizations. In the category of 50 μm, the multimode optical fibers can be further classified by an ISO 11081 standard into four types, that is, OM1, OM2, OM3 and OM4 according to bandwidths. The transmission speed of a 50 μm multimode fiber optic system varies from 10 Mbit/s to 10 Gbit/s even 100 Gbit/s, and the maximum link distance can reach as far as 2 km, which is more than sufficient to meet application demands thereof. However, the multimode optical fibers applied to systems of 10 Gbit/s or even 100 Gbit/s are all transmitted in a window of 850 nm, owing to the invention and the reduction of cost of the VCSEL850 nm laser. If the cost of the optical devices is reduced in the window of 1300 nm, transmission of a multimode system at a speed of 10 Gbit/s or even 100 Gbit/s in the window is entirely possible; and low loss characteristics of the optical fibers in the window may be fully used to greatly increase the transmission distance and reduce the system cost. In the past few years, long-wavelength VCSEL manufacturers have done a lot of reliability tests, and have released the test results of 1300 nm band VCSEL fabricated with a wafer bonding method as follows: a zero fault rate of a 5000-hour high-temperature accelerated aging experiments is achieved, and the mean time to failure is thirty million hours at the temperature of 25° C., and is two million hours at the temperature of 70° C.
Multimode optical fibers, especially multimode optical fibers with high transmission performance, such as OM3 or OM4 optical fibers, are widely used in the short-medium distance fiber optic network systems. When the optical fibers are used in buildings or miniaturized devices, space is limited; the optical fibers endure a high bending stress. If the optical fibers endure a great bending stress for a long term, life of the optical fibers may be reduced, and transmission performance indexes may be worsened; therefore, it is required that the optical fibers be bending-resistant, so as to meet the need of special applications. An effective way to reduce the additional bending loss of an optical fiber is to optimize the cross-sectional structure of the optical fiber, mainly to design claddings with different structures, so as to reduce the loss of optical power when the optical fiber bends.
In addition, to let a multimode optical fiber have a good bandwidth, the refractive index profile of the optical fiber core should be a perfect parabola. Many literatures including Patent CN183049C only focus on how to prepare a preform with an accurate refractive index profile; however, in the process of fiber drawing of the preform, due to residual stress and composition diffusion, the refractive index of the optical fiber is greatly distorted compared with the preform, thereby reducing the bandwidth of the optical fiber. Therefore, optical fiber refractive index profile distortion remains to be further addressed.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.